Display device

ABSTRACT

One embodiment of the present invention provides a highly reliable display device. In particular, a display device to which a signal or a power supply potential can be supplied stably is provided. Further, a bendable display device to which a signal or a power supply potential can be supplied stably is provided. The display device includes, over a flexible substrate, a display portion, a plurality of connection terminals to which a signal from an outside can be input, and a plurality of wirings. One of the plurality of wirings electrically connects one of the plurality of connection terminals to the display portion. The one of the plurality of wirings includes a first portion including a plurality of separate lines and a second portion in which the plurality of lines converge.

TECHNICAL FIELD

The present invention relates to a display device. In particular, oneembodiment of the present invention relates to a display deviceincluding a bendable display portion.

BACKGROUND ART

In recent years, diversification of the shape of electronic deviceshaving a display function has been required. For example, an electronicdevice including a display device in which a display element is providedover a flexible substrate that is bendable and can display images on thecurved surface is demanded. This display device is also called aflexible display and is under development for practical application.

An organic electroluminescence (EL) element, a liquid crystal element,or the like can be used as a display element for flexible displays. Theflexible display is, for example, an electronic paper including anelement that performs display by an electrophoretic method or anelectronic liquid powder method.

For example, Patent Document 1 discloses an organic EL display panel inwhich an organic EL element is provided over a resin substrate made of aflexible film.

REFERENCE Patent Document

[Patent Document 1] International Publication No. 2006/046679

DISCLOSURE OF INVENTION

In an electronic device in which a display device is incorporated, aconnection wiring that electrically connects a housing to the displaydevice needs to be attached to the display device to supply a signal ora power supply potential to the display device. A typical example of theconnection wiring is a flexible printed circuit (FPC). To attach an FPCto a substrate, thermocompression bonding is employed with ananisotropic conductive film (ACF) or the like.

However, a display device including a display element over a flexiblesubstrate has a problem in that the substrate or a wiring provided overthe substrate may be destroyed by heat or pressure applied bythermocompression bonding. Further, the display device also has aproblem in that the connection wiring peels from the substrate bycurving the substrate.

An object of one embodiment of the present invention is to provide ahighly reliable display device. In particular, an object is to provide adisplay device to which a signal or a power supply potential can besupplied stably. Further, an object is to provide a bendable displaydevice to which a signal or a power supply potential can be suppliedstably.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all the above-described objects. Other objects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

One embodiment of the present invention is a display device including aflexible substrate, a display portion over the flexible substrate, aplurality of connection terminals to which a signal from an outside canbe input over the flexible substrate, and a plurality of wirings overthe flexible substrate. In the display device, one of the plurality ofwirings electrically connects one of the plurality of connectionterminals to the display portion. The one of the plurality of wiringsincludes a first portion including a plurality of separate lines intowhich the wiring is separated and a second portion in which theplurality of lines converge.

In the display device of one embodiment of the present invention, thefirst portion of the wiring preferably has a smaller thickness than thesecond portion.

Further in the display device of one embodiment of the presentinvention, the first portion of the wiring preferably has a largerthickness than the second portion.

Further in the display device of one embodiment of the presentinvention, the flexible substrate is preferably bent in a regionoverlapping with the first portion of the wiring.

Further in the display device of one embodiment of the presentinvention, it is preferable that a bending direction of the flexiblesubstrate is not the same as an extending direction of the wiring in thefirst portion.

Further the display device of one embodiment of the present inventionpreferably includes an IC over the flexible substrate. In the displaydevice, another one of the plurality of wirings electrically connectsthe IC to the display portion, and the IC is preferably provided betweenthe first portion of the wiring and the connection terminal.

In this specification and the like, “to bend a surface” refers toshaping a surface that is flat so that a line on the shaped surface thatconnects arbitrary two points on the surface is continuously gradient.The curvature radius at an arbitrary point on the bent surface isgreater than 0.

Further in this specification and the like, a bendable device refers toa device that does not lost its specific function when part of thedevice is bent at a predetermined curvature radius. For example, abendable display device refers to a display device that can performdisplay even when part of the display device is bent.

With one embodiment of the present invention, a highly reliable displaydevice can be provided. Further, a display device to which a signal or apower supply potential can be supplied stably can be provided. Further,a bendable display device to which a signal or a power supply potentialcan be supplied stably can be provided.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B illustrate a structural example of a display device ofone embodiment;

FIGS. 2A and 2B illustrate structural examples of wirings provided in adisplay device of one embodiment;

FIGS. 3A and 3B illustrate structural examples of a display device ofone embodiment;

FIGS. 4A to 4C illustrate structural examples of wirings provided in adisplay device of one embodiment;

FIGS. 5A to 5C illustrate structural examples of a display device of oneembodiment;

FIGS. 6A to 6D illustrate structural examples of wirings provided in adisplay device of one embodiment;

FIGS. 7A to 7D illustrate structural examples of a display device of oneembodiment;

FIGS. 8A to 8F illustrate an example of a method for manufacturing adisplay device of one embodiment;

FIG. 9 illustrates a structural example of a display device of oneembodiment;

FIG. 10 illustrates a structural example of a display device of oneembodiment; and

FIGS. 11A to 11C illustrate structural examples of an electronic deviceof one embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the description below, andit is easily understood by those skilled in the art that various changesand modifications can be made without departing from the spirit andscope of the present invention. Therefore, the present invention shouldnot be interpreted as being limited to the description of theembodiments below.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and description of suchportions is not repeated. Further, the same hatching pattern is appliedto portions having similar functions, and the portions are notespecially denoted by reference numerals in some cases.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of components is exaggerated for clarityin some cases. Therefore, the size of components is not limited to therelative size in the drawing.

Note that in this specification and the like, the expression“electrically connected” includes the case where components areconnected through an “object having any electric function”. There is noparticular limitation on an “object having any electric function” aslong as electric signals can be transmitted and received betweencomponents that are connected through the object. Examples of the“object having any electric function” include an electrode, a wiring, aswitching element such as a transistor, a resistor, a coil, a capacitor,an element with a variety of functions, and a circuit with a variety offunctions.

Embodiment 1

In this embodiment, configuration examples of a display device of oneembodiment of the present invention will be described with reference todrawings.

Configuration Example of Display Device

FIG. 1A is a schematic top view of a display device 100 of oneembodiment of the present invention.

The display device 100 includes a display portion 102, a plurality ofwirings 111, a plurality of connection terminals 112, an IC 113, and aplurality of wirings 114 over a flexible substrate 101.

The display portion 102 includes a pixel portion 103 and a drivercircuit 104.

In the pixel portion 103, pixels each including a display element arearranged in a matrix. By driving each pixel, an image can be displayedon the pixel portion 103.

As a display element that can be used in a pixel, an organicelectroluminescence (EL) element, a liquid crystal element, or the likecan be used. Alternatively, an element that performs display by anelectrophoretic method, an electronic liquid powder method, or the likemay be included in the pixel.

Using an organic EL element as a display element provided in a pixel ispreferable because a backlight is not required. When a backlight isrequired in the case of using a liquid crystal element as a displayelement, a flexible backlight is attached to the side of the substrate101 that is opposite to the side provided with the display portion 102,so that the backlight can be bent in accordance with bending of thesubstrate 101.

The driver circuit 104 is a circuit that drives the pixels in the pixelportion 103 and may be a circuit having a function of a gate drivercircuit, for example. The driver circuit 104 preferably consists ofsemiconductor elements such as thin film transistors formed over thesubstrate 101. Note that the driver circuit 104 is not necessarilyprovided over the substrate 101, and the IC 113 may have the function ofthe driver circuit 104.

The substrate 101 has a shape including a projecting part as illustratedin FIG. 1A. Over the projecting part of the substrate 101, part of theplurality of wirings 111, the plurality of connection terminals 112, theIC 113, and the wirings 114 are provided.

The connection terminals 112 are input terminals of various signals fordriving the display portion 102, such as a power supply voltage, animage signal, or a timing signal from the outside.

The IC 113 is a circuit that drives the display portion 102 and may be acircuit having a function of a source driver circuit, for example.Alternatively, the IC 113 may be a circuit that has a function ofperforming image processing on the input image signal to generate a newimage signal. As illustrated in FIG. 1A, it is preferable to provide theIC 113 over the substrate 101. Note that the IC 113 is not necessarilyprovided over the substrate 101. For example, the IC 113 may be providedoutside the display device 100 so that an output signal of the IC 113 isinput to the display device 100 through the connection terminals 112 andthe wirings 111.

One of the plurality of wirings 114 is a wiring that electricallyconnects one of the plurality of connection terminals 112 to the IC 113.Signals for driving the IC 113 or the display portion 102 are input tothe connection terminals 112 to which the wirings 114 are electricallyconnected. Note that when the IC 113 is not provided, the wirings 114are unnecessary.

The wirings 111 are wirings arranged between the connection terminals112 and the display portion 102. The wirings 111 are electricallyconnected to the display portion 102, and signals for driving thedisplay portion 102 can be input to the display portion 102 through thewirings 111. Although the number of wirings 111 illustrated in FIGS. 1Aand 1B is small for simplicity, the practical number of wirings 111 isusually more than the illustrated number.

Some of the wirings 111 each directly and electrically connect theconnection terminal 112 to the display portion 102, while the otherseach electrically connects the IC 113 to the display portion 102. Allthe wirings 111 have a common function of transmitting a signal fordriving the display portion 102 to the display portion 102. Accordingly,these wirings are collectively referred to as the wirings 111 in thefollowing description.

The signals input to the connection terminals 112 that are electricallyconnected to the display portion 102 through the wirings 111 are, forexample, a signal for driving the driver circuit 104 and a signalincluding a voltage that is different from the power supply voltage fordriving the IC 113.

In the structure illustrated in FIG. 1A, the IC 113 is provided betweenthe connection terminals 112 and the display portion 102, and the numberof wirings 114 between the connection terminals 112 and the IC 113 isnot equal to the number of wirings 111 between the IC 113 and thedisplay portion 102.

In the display device 100, the substrate 101 can be bent at a bendingportion 110 illustrated in FIG. 1A that overlaps with the wirings 111,and the portion of the substrate 101 over which the connection terminals112 and the IC 113 are provided can be bent and folded toward the rearside of the display surface.

FIG. 1B schematically illustrates the display device 100 in which thesubstrate 101 is bent and folded at the bending portion 110. In FIG. 1B,the display portion 102 is also bent in a concave curve.

As illustrated in FIG. 1B, the projecting portion of the substrate 101,over which the connection terminals 112 and the IC 113 are provided, canbe bent and folded toward the rear side of the display surface. Thisallows a reduction in the area of the display device 100 that is visiblewhen looking at the display surface side, and the display device 100 canhave a shorter side frame. Accordingly, in the case of using the displaydevice 100 in an electronic device, for example, miniaturization of theelectronic device can be achieved.

Further, the connection terminals 112 provided on the folded projectingportion of the substrate 101 can be connected to a connector provided ina housing of the electronic device, for example. In other words, part ofthe display device 100 can function as an FPC. In this way, thepossibility of causing problems that might occur when an FPC is attachedto a flexible display device, such as the destruction of the substrateor the wirings provided over the substrate or peeling of the FPC whenthe substrate 101 is bent, can be eliminated, for example. Thus, anextremely highly reliable display device can be obtained.

Further, in the display device 100, the display portion 102 can be bentin a concave curve as illustrated in FIG. 1B or in a convex curve. Theimage can be displayed on the curved surface. In this case, a variety ofimage expressions or applications that a display device with a flatdisplay surface cannot exhibit can be exhibited.

Furthermore, a flexible touch sensor may be provided so as to overlapwith the display portion 102.

Wiring Shape

Next, examples of the shape of the wirings 111 will be described. FIG.2A is a top view schematically illustrating part of two parallel wirings111.

Openings are provided in part of each wiring 111 and separate the wiring111 into a plurality of lines. In other words, each of the wirings 111includes a first portion 121 including the plurality of separate linesand a second portion 122 in which the plurality of lines converge.

When part of the substrate 101 is bent, it is preferable that thebending portion 110 overlap with the first portion 121.

In the case of bending a portion where a wiring that transmits a signalto the display portion 102 is provided, a crack may occur in the wiringby stress caused by the bending and in the worst case a break of thewiring may occur. When a break of the wiring occurs, a signal cannot betransmitted to the display portion 102, leading to a display defect.

However, when the wiring 111 that crosses over the bending portion 110has the above-described shape, even if one of the plurality of separatedlines is broken, the other lines can transmit a signal. Thus, a displaydefect caused by bending is prevented and the display device 100 withhigh reliability can be provided.

Further, as illustrated in FIG. 2B, the line width of each of theplurality of separate lines in the first portion 121 of the wiring 111is preferably as large as possible. With this shape, an increase inresistance caused by separation of the wiring 111 can be prevented.Moreover, even when one or more lines of the plurality of separate linesare broken, an increase in resistance can be prevented; accordingly, aninfluence of a signal delay or the like can be reduced.

The wirings 111 are each divided into three lines in FIGS. 2A and 2B;however, other than three lines, the wirings 111 may be each dividedinto two or more lines. A larger number of separate lines lower the riskof wiring breaks that may occur when the wiring is bent.

When the wirings 111 have the above-described shapes, the curvatureradius at the bending portion 110 of the substrate 101 can be setsmaller, and the substantial thickness of the display device 100 inwhich part of the substrate 101 is bent toward the rear side can besmall. The allowable curvature radius at the midpoint position of thewhole thickness of the display device 100 in the bending portion 110 canbe as small as 0.1 mm or more and 10 mm or less, preferably 0.5 mm ormore and 5 mm or less, further preferably 0.5 mm or more and 2 mm orless.

Here, examples of the cross-sectional structure of the bending portion110 in the display device 100 in the bent state in FIG. 1B will bedescribed with reference to FIGS. 3A and 3B.

FIG. 3A schematically illustrates a cross section of the bending portion110 in the display device 100. In FIG. 3A, a region including the wiring111, the IC 113, the wiring 114, and the connection terminal 112 isshown.

In FIG. 3A, the wiring 111 is formed over the substrate 101, and aflexible substrate 131 is provided over the wiring 111 with an adhesivelayer 132 interposed therebetween.

In order to electrically connect the wiring 111 and the wiring 114 tothe IC 113, an end portion of the wiring 111 and an end portion of thewiring 114 are exposed by providing an opening in the substrate 131 andthe adhesive layer 132 that are positioned on the wiring 111 and thewiring 114. In the opening, bumps 134 of the IC 113 are electricallyconnected to the wiring 111 or the wiring 114 through an ACF 133.

Furthermore, another opening is provided in the substrate 131 and theadhesive layer 132 that are positioned on part of the wiring 114; thus,a top surface of the wiring 114 is exposed. The exposed part of thewiring 114 functions as the connection terminal 112.

Here, the first portion 121 and the second portion 122 in the wiring 111preferably have different thicknesses.

FIG. 3A illustrates a case where the thickness of the first portion 121is smaller than that of the second portion 122 in the wiring 111.

In the bending portion 110, the stress applied by bending varies betweenthe upper side and the lower side of the thickness direction of thewiring 111. By thinning the first portion 121 of the wiring 111 in theregion overlapping with the bending portion 110, the difference in thestress applied by bending between the upper side and the lower side canbe reduced, which can lower the risk of breaking the wiring 111.

It is preferable to use a low-resistant conductive material such as Cufor the first portion 121 because the wiring resistance might increasewhen the first portion 121 of the wiring 111 is thinned. The firstportion 121 and the second portion 122 of the wiring 111 may be made ofdifferent materials or may be made of the same material.

Further, it is preferable that the line width of the first portion 121be larger than that of the second portion 122 in the wiring 111 becausean increase in wiring resistance can be prevented. In the case where theseparate lines are included in the first portion 121 of the wiring 111,the top view as illustrated in FIG. 2B can be used to effectivelyprevent an increase in wiring resistance.

FIG. 3B illustrates a case where the thickness of the first portion 121is larger than that of the second portion 122 in the wiring 111.

By thickening the first portion 121 of the wiring 111 in the regionoverlapping with the bending portion 110, the mechanical strength of thewiring 111 can be increased, which can prevent a break of the wiring 111when the wiring 111 is bent.

In the case where the wiring 111 is separated into a plurality of linesin the first portion 121 as illustrated in the top view of FIG. 2A, thethickness of the first portion 121 is set large, so that an increase inwiring resistance can be prevented.

Although FIGS. 3A and 3B illustrate the cases in which the substrate 131is provided over the wiring 111 with the adhesive layer 132 interposedtherebetween, the configuration is not limited to these configurationsas long as a surface of the wiring 111 is insulated without beingexposed. For example, when the surface of the wiring 111 is insulated byforming a resin over the wiring 111, it is possible to reduce thethickness of the display device 100 in the region where the wiring 111is provided; accordingly, the display device can be easily bent. Furtherin this case, by removing the resin over part of the wiring 111 or thewiring 114 to expose a surface thereof, part of the wiring 111 or thewiring 114 can function as the connection terminal 112.

FIGS. 4A to 4C illustrate schematic cross-sectional views of part of thewiring 111.

In the case where the thickness of the first portion 121 is setdifferent from that of the second portion 122 in the wiring 111, thethick portion and the thin portion may be formed of a single layer ofthe same material as illustrated in FIG. 4A. In this case, the thinportion may be formed by removing part of an upper portion of the wiringby etching (also referred to as half etching).

Alternatively, the thick portion may be formed of stacked layersincluding two or more layers, and the thin portion may be formed of oneor more layers obtained by removing one or more layers from the abovestacked layers.

FIGS. 4B and 4C are schematic cross-sectional views in which the thickportion of the wiring 111 has stacked layers of a wiring 111 a and awiring 111 b.

As illustrated in FIG. 4B, the thin portion of the wiring 111 may beformed by stacking the wiring 111 a over the wiring 111 b and thenremoving part of the wiring 111 a by etching. At this time, it ispreferable to use different materials for the wiring 111 a and thewiring 111 b because unintended etching of an upper portion of thewiring 111 b at the time of etching the wiring 111 a can be prevented;thus, the thickness of the wiring 111 b does not become smaller than theintended thickness.

As illustrated in FIG. 4C, the thick portion of the wiring 111 may beformed by removing part of the wiring 111 b by etching and thenproviding the wiring 111 a so as to cover an end portion of the wiring111 b. This configuration is preferable because defects are not causedby etching even when the same material is used for the wiring 111 a andthe wiring 111 b.

Here, it is preferable that a material used for the first portion 121 ofthe wiring 111 contain a highly ductile or highly malleable material. Itis particularly preferable to use a material having both a highductility and a high malleability. When the wiring over the bendingportion 110 has a high ductility, a break of the wiring 111 does noteasily occur by bending. When the wiring has a high malleability, acrack does not easily occur in the wiring 111 when the wiring 111 isreturned to a flat state from the bent state. Examples of the materialhaving both a high ductility and a high malleability include a metalmaterial such as gold, silver, platinum, iron, nickel, copper, aluminum,zinc, and tin and an alloy containing this metal material.

In the case where the first portion 121 of the wiring 111 has stackedlayers of two or more layers, by using the above material for at leastone of the layers, preferably for all of the layers, a break or a crackof the wiring 111 can be prevented.

The wiring shape has been described so far.

Other Configuration Examples of Display Device

Configuration examples of a display device that are different from thatof the display device 100 illustrated in FIGS. 1A and 1B will bedescribed below.

FIG. 5A illustrates an example of the display device 100 in which the IC113 is not incorporated.

In the display device 100 illustrated in FIG. 5A, the IC 113 and thewiring 114 are not provided. In addition, the display portion 102 isdirectly and electrically connected to the connection terminals 112through the wirings 111.

FIG. 5B illustrates an example in which the bending portion 110 islocated not in the projecting portion of the substrate 101 but in aportion close to the display portion 102. This configuration allows afurther reduction in the area of the display device 100 that is visiblewhen looking at the display surface side, and the display device 100 canhave a shorter side frame.

FIG. 5C illustrates a configuration in which the wirings 111 arearranged so that the bending direction of the substrate 101 is not thesame as the extending direction of the wirings 111 in a region where thewirings 111 and the bending portion 110 cross each other. In otherwords, the wirings 111 are provided so as to obliquely cross the bendingportion 110.

The bending direction and the extending direction of the wirings 111will be explained with reference to FIGS. 6A to 6D.

First, the bending direction of a surface will be explained withreference to FIG. 6A. When a surface is bent without expansion andcontraction, a tangent line 142 at an arbitrary point on a formed curvedsurface 141 that is tangential to the curved surface 141 is determinedas having no alternative. Here, the direction that is perpendicular tothe tangent line 142 and along the tangent plane to the curved surfaceat the arbitrary point is a bending direction 143, as indicated by adashed-and-dotted line arrow in FIG. 6A.

As illustrated in FIG. 6B, once two arbitrary points on the curvedsurface 141 are designated, the shortest line 144 that connects thesetwo points on the curved surface is determined as having no alternative.In the case where the line 144 crosses the tangent line 142 at rightangles on an arbitrary point on the line 144, the bending direction ofthe curved surface 141 is the same as the extending direction of theline 144.

An angle formed between the tangent line 142 and the shortest line 144that connects arbitrary two points on the curved surface 141 along thecurved surface 141 is the same at any point on the line 144. Since thetangent line 142 and the bending direction 143 always cross each otherat right angles, an angle obtained by subtracting an acute angle(including 90 degrees) formed between the line 144 and the tangent line142 from 90 degrees is referred to as an angle formed between theextending direction of the line 144 and the bending direction of thecurved surface 141. FIG. 6B illustrates the case where the angle formedbetween the extending direction of the line 144 and the bendingdirection of the curved surface 141 is 0 degree.

FIGS. 6C and 6D each illustrate the wiring 111 when a surface 145 onwhich the wiring 111 is formed is bent.

FIG. 6C illustrates the arrangement of the wiring 111, where theextending direction of the wiring 111 is the same as (is parallel with)the bending direction of the surface 145.

In this case, the curvature radius of the wiring 111 along the extendingdirection is the smallest and is equal to that of the surface 145.

FIG. 6D illustrates the arrangement of the wiring 111, where theextending direction of the wiring 111 is not the same as the bendingdirection of the surface 145.

In other words, the wiring 111 is arranged so that the angle formedbetween the extending direction of the wiring 111 and the bendingdirection is larger than 0 degree.

The angle formed between the extending direction of the wiring 111 andthe bending direction may be, for example, greater than or equal to 5degrees and less than 90 degrees, preferably greater than or equal to 15degrees and less than or equal to 60 degrees, and further preferablygreater than or equal to 30 degrees and less than or equal to 60degrees.

In this case, the curvature radius of the wiring 111 along the extendingdirection is larger than that of the surface 145. Accordingly, the riskof destruction or a break of the wiring 111 when the surface 145 is bentcan be lowered, and a highly reliable display device can be provided.

In addition, the surface 145 (or the substrate 101) can be bent at acurvature radius that is smaller than the curvature radius at whichdestruction or a break of the wiring 111 might occur when the wiring 111is bent. Accordingly, the substantial thickness of the display device100 in which part of the substrate 101 is bent and folded toward therear side can be small.

Next, configuration examples of the display device other than the aboveexamples will be described with reference to FIGS. 7A to 7D.

FIG. 7A illustrates an example in which two driver circuits (drivercircuits 104 a and 104 b) between which the pixel portion 103 ispositioned are provided instead of the driver circuit 104 provided closeto the projecting portion of the substrate 101 in FIG. 1A. Thisconfiguration including two separate driver circuits is particularlypreferable in the case where the pixel portion 103 in the display devicehas high definition.

Depending on the type of the electronic device in which the displaydevice 100 is incorporated, the display portion 102 is configured tobend at a certain position. For example, in an electronic device thatcan be folded at a predetermined position, the display portion 102 isrepeatedly bent always at the same position. In this case, the drivercircuits 104 a and 104 b repeatedly change between the flat state andthe bent state, which may degrade electric characteristics of elementssuch as transistors included in the driver circuit 104 a and the drivercircuit 104 b.

It is preferable to divide the driver circuit such that an areaoverlapping with the bending portion 120 of the display portion 102 issandwiched between the divided driver circuits as illustrated in FIG.7B. In FIG. 7B, the driver circuit 104 a in FIG. 7A is divided intothree driver circuits (driver circuit 104 c, driver circuit 104 d,driver circuit 104 e). A bonding portion 120 is provided between thedriver circuit 104 c and the driver circuit 104 d, and another bondingportion 120 is provided between the driver circuit 104 d and the drivercircuit 104 e. Similarly, the driver circuit 104 b in FIG. 7A is dividedinto a driver circuit 104 f, a driver circuit 104 g, and a drivercircuit 104 h.

FIG. 7C is an enlarged view of a region surrounded by a broken line inFIG. 7B. Two divided driver circuits (driver circuit 104 c, drivercircuit 104 d) and a plurality of pixels 150 arranged in a matrix andelectrically connected to either of the driver circuits are illustratedin FIG. 7C.

A variety of signals for driving the driver circuit 104 d input from thewirings 111 can be input to the driver circuit 104 d through a pluralityof wirings 151 provided between the driver circuit 104 c and the drivercircuit 104 d. At this time, the distance between circuit elements(e.g., shift registers, buffers) in the driver circuit 104 c and thedriver circuit 104 d is shorter than the distance between the pixels150.

Further, the configuration illustrated in FIG. 7D in which part of thedriver circuit 104 c and part of the driver circuit 104 d are providedto extend toward the outside may be employed. With this configuration,the distance between the circuit elements (shift registers, buffers) inthe driver circuit 104 c and the driver circuit 104 d is not shortenedand can be set similar to the distance in the case where the drivercircuit is not divided. This configuration is particularly effective fora high-definition display device including the pixels 150.

Although the driver circuit divided into three parts has been describedhere, the division number of the driver circuit may be two or four ormore without being limited to three.

Other configuration examples of the display device have been describedso far.

This embodiment can be implemented in combination with any of the otherembodiments disclosed in this specification as appropriate.

Embodiment 2

An example of a method for manufacturing a display device of oneembodiment of the present invention will be described below.

Example of Manufacturing Method Formation of Separation Layer

First, a separation layer 202 is formed over a supporting substrate 201.

As the supporting substrate 201, a substrate having heat resistance toat least the heat applied in a subsequent process is used. Examples ofthe supporting substrate 201 include a glass substrate, a resinsubstrate, a semiconductor substrate, a metal substrate, and a ceramicsubstrate.

As a material of the separation layer 202, a high melting point metalmaterial such as tungsten, titanium, or molybdenum can be used, forexample. Tungsten is preferably used.

The separation layer 202 can be formed by a sputtering method, forexample.

Formation of Another Separation Layer and Oxide Layer

Then, a separation layer 203 is formed over the separation layer 202. Anoxide layer 211 is formed between the separation layer 202 and theseparation layer 203.

As a material of the separation layer 203, an inorganic insulatingmaterial such as silicon oxide, silicon oxynitride, silicon nitrideoxide, silicon nitride, or aluminum oxide can be used. The separationlayer 203 can be a single layer or stacked layers containing the aboveinorganic insulating material.

The separation layer 203 has particularly preferably a stacked structureincluding two or more layers in which at least the layer closest to theseparation layer 202 is a layer that releases hydrogen by being heated.For example, the separation layer 203 has a stacked structure includinga layer containing silicon oxynitride and a layer containing siliconnitride from the separation layer 202 side.

Note that in this specification and the like, “silicon oxynitride”contains more oxygen than nitrogen, meanwhile, “silicon nitride oxide”contains more nitrogen than oxygen.

The separation layer 203 can be formed by a film formation method suchas a sputtering method or a plasma CVD method. In particular, theseparation layer 203 is preferably formed by a plasma CVD method using adeposition gas containing hydrogen.

Here, a surface of the separation layer 202 is oxidized at the time offormation of the separation layer 203, whereby the oxide layer 211 canbe formed between the separation layer 202 and the separation layer 203.

The oxide layer 211 is a layer containing an oxide of the metal that iscontained in the separation layer 202. The oxide layer 211 is preferablya layer containing tungsten oxide.

Tungsten oxide is generally represented by WO_((3-x)) and is anon-stoichiometric compound that can have a variety of compositions,typically WO₃, W₂O₅, W₄O₁₁, and WO₂. Titanium oxide TiO_((2-x)) andmolybdenum oxide MoO_((3-x)) are also non-stoichiometric compounds.

The oxide layer 211 at this stage preferably contains a large amount ofoxygen. For example, in the case where tungsten is used for theseparation layer 202, the oxide layer 211 is preferably a tungsten oxidelayer containing WO₃ as its main component.

The oxide layer 211 can be formed on the surface of the separation layer202 in advance by performing plasma treatment on the surface of theseparation layer 202 in an atmosphere containing a dinitrogen monoxidegas before formation of the separation layer 203. When such a method isemployed, the thickness of the oxide layer 211 can vary depending on theconditions of the plasma treatment, and the thickness of the oxide layer211 can be controlled more effectively than in the case where plasmatreatment is not performed.

The thickness of the oxide layer 211 is, for example, more than or equalto 0.1 nm and less than or equal to 100 nm, preferably more than orequal to 0.5 nm and less than or equal to 20 nm. Note that the oxidelayer 211 with an extremely small thickness cannot be observed in across-sectional image in some cases.

FIG. 8A illustrates a schematic cross-sectional view at this stage.

Heat Treatment

Next, heat treatment is performed to change the quality of the oxidelayer 211.

By the heat treatment, hydrogen is released from the separation layer203 to the oxide layer 211.

The metal oxide in the oxide layer 211 is reduced by hydrogen suppliedto the oxide layer 211, so that a plurality of regions with differentproportions of oxygen are mixed in the oxide layer 211. For example, inthe case where tungsten is used for the separation layer 202, WO₃ in theoxide layer 211 is reduced to generate an oxide with proportion ofoxygen lower than that of WO₃ (e.g., WO₂), resulting in a state whereWO₃ and the oxide with the lower proportion of oxygen are mixed. Thecrystal structure of such a metal oxide depends on the proportion ofoxygen; thus, when a plurality of regions with different proportions ofoxygen are provided in the oxide layer 211, the mechanical strength ofthe oxide layer 211 is reduced. As a result, the oxide layer 211 islikely to be damaged inside, so that the separation property in a laterseparation step can be increased.

The heat treatment may be performed at a temperature higher than orequal to the temperature at which hydrogen is released from theseparation layer 203 and lower than the temperature at which thesupporting substrate 201 is softened. Further, the heat treatment ispreferably performed at a temperature higher than or equal to thetemperature at which a reduction reaction between hydrogen and the metaloxide in the oxide layer 211 occurs. For example, in the case wheretungsten is used for the separation layer 202, the heating temperatureis higher than or equal to 420° C., higher than or equal to 450° C.,higher than or equal to 600° C., or higher than or equal to 650° C.

The higher the temperature of the heat treatment is, the more the amountof hydrogen released from the separation layer 203 can be, leading toimproved separation property. However, even when the heating temperatureis lowered in consideration of the heat resistance of the supportingsubstrate 201 and the productivity, a high separation property can beachieved by forming the oxide layer 211 in advance by performing plasmatreatment on the separation layer 202 as described above.

Formation of Display Portion and Wirings

Next, the display portion 102, the wiring 111, and the wiring 114 areformed over the separation layer 203 (FIG. 8B).

The display portion 102 includes at least a display element, and mayadditionally include a wiring that is electrically connected to thedisplay element or a transistor used in a circuit that controls drivingof the display element.

In the case of manufacturing a bottom-gate transistor as the transistorincluded in the display portion 102, a gate electrode, a gate insulatinglayer, a semiconductor layer, and a source and drain electrodes may beformed in this order over the separation layer 203.

Note that the structure of the transistor may be a forward staggeredtransistor, an inverted staggered transistor, or the like.Alternatively, a top-gate transistor or a bottom-gate transistor may beused. In addition, a channel-etched transistor or a channel protectivetransistor may be used. In the case of a channel protective transistor,a channel protective film may be provided only over a channel region.Alternatively, an opening may be formed only in a portion where a sourceand drain electrodes are in contact with a semiconductor layer and achannel protective film may be provided in an area other than theopening.

As a semiconductor applicable to a semiconductor layer in which achannel of a transistor is formed, for example, a semiconductor materialsuch as silicon or germanium, a compound semiconductor material, anorganic semiconductor material, or an oxide semiconductor material maybe used.

Further, there is no particular limitation on the crystallinity of asemiconductor used for the transistor, and an amorphous semiconductor ora semiconductor having crystallinity (a microcrystalline semiconductor,a polycrystalline semiconductor, a single crystal semiconductor, or asemiconductor partly including crystal regions) may be used. Asemiconductor having crystallinity is preferably used, in which casedeterioration of transistor characteristics can be reduced.

For example, in the case of using silicon as the semiconductor,amorphous silicon, microcrystalline silicon, polycrystalline silicon,single crystal silicon, or the like can be used.

In the case of using an oxide semiconductor as the semiconductor, anoxide semiconductor containing at least one of indium, gallium, and zincis preferably used. Typically, an In—Ga—Zn-based metal oxide can begiven. An oxide semiconductor having a wider band gap and a lowercarrier density than silicon is preferably used, in which case off-stateleakage current can be reduced.

As the display element provided in the display portion 102, alight-emitting element in which a layer containing a light-emittingorganic compound is interposed between a pair of electrodes is formedover the separation layer 203, so that a flexible light-emitting devicecan be manufactured. For example, a flexible lighting device (or a lightsource) including a light-emitting element can be manufactured, or animage display device may be manufactured by forming a plurality ofpixels including transistors and display elements such as light-emittingelements or liquid crystal elements over the separation layer 203.Examples of the flexible image display device will be described in laterembodiment.

Here, the wiring 111 and the wiring 114 are preferably formed byprocessing the same layer that forms a wiring and an electrode includedin the display portion 102. As examples of the wiring and the electrodeincluded in the display portion 102, a gate electrode, a sourceelectrode, and a drain electrode of a transistor, an electrode includedin a light-emitting element, and a wiring that electrically connects thetransistor to the light-emitting element can be given.

FIG. 8B illustrates an example in which the wiring 111 has a stackedstructure including the wiring 111 a and the wiring 111 b. In the wiring111, a portion where only the wiring 111 a is formed corresponds to thefirst portion, and a portion where the wiring 111 a and the wiring 111 bare stacked corresponds to the second portion. The wiring 114 has thesame structure as the second portion of the wiring 111. In this case,the wiring 111 b can be formed using the same material as that of thegate electrode of the transistor, and the wiring 111 a can be formedusing the same material as that of the source or drain electrode of thetransistor, for example. Thus, the wiring 111 can be formed withoutincreasing the steps.

Bonding

Next, the supporting substrate 201 and the substrate 131 are bonded toeach other by the adhesive layer 132 (FIG. 8C).

As the substrate 131, a flexible substrate is preferably used. Forexample, a metal substrate or a glass substrate which is thin enough tohave flexibility can be used as well as a resin such as polyethyleneterephthalate (PET) or polyethylene naphthalate (PEN). A compositematerial in which two or more of a metal, glass, and a resin are stackedcan also be used.

In the case of using a resin as the substrate 131, a barrier layer thatdoes not easily transmit impurities such as water is preferably providedon either surface of the substrate 131. For example, a layer of siliconoxide, silicon oxynitride, silicon nitride oxide, silicon nitride,aluminum oxide, or the like may be provided.

A thermosetting resin or an ultraviolet curable resin can be used forthe adhesive layer 132 as long as the resin can firmly bond surfaces tobe bonded. For example, an acrylic resin, a urethane resin, an epoxyresin, or a resin having a siloxane bond can be used. In the case wherethe substrate 131 is removed later, a water-soluble resin, a resinsoluble in an organic solvent, or the like can be used.

Separation

Next, the separation layer 202 and the separation layer 203 areseparated from each other at the oxide layer 211 (FIG. 8D).

For the separation, for example, the supporting substrate 201 or thesubstrate 131 is fixed to a suction stage and a separation startingpoint is formed between the separation layer 202 and the separationlayer 203. The separation starting point may be formed by, for example,inserting a sharp instrument such as a knife between the layers.Alternatively, the separation starting point may be formed byirradiating part of the separation layer 202 with laser light to melt,vaporize, or thermally destroy the part of the separation layer 202.Further alternatively, the separation starting point may be formed bydripping liquid (e.g., alcohol, water, or water containing carbondioxide) onto an end portion of the separation layer 202 so that theliquid penetrates into an interface between the separation layer 202 andthe separation layer 203 by using capillary action.

Then, physical force is gently applied to the area where the separationstarting point is formed in a direction substantially perpendicular tothe bonded surfaces, so that separation can be caused without damage tothe separation layer 203. At this time, separation may be caused byattaching tape or the like to the supporting substrate 201 or thesubstrate 131 and pulling the tape in the aforementioned direction, orseparation may be caused by pulling an end portion of the supportingsubstrate 201 or the substrate 131 with a hook-like member.Alternatively, separation may be caused by pulling an adhesive member ora member capable of vacuum suction attached to the back side of thesupporting substrate 201 or the substrate 131. Further alternatively,separation may be caused by pressing an adhesive roller to the back sideof the supporting substrate 201 or the substrate 131 and rolling andmoving the roller.

Here, if separation is performed in such a manner that liquid containingwater such as water or an aqueous solution is added to the separationinterface and the liquid penetrates into the separation interface, theseparation property can be improved.

The separation is mainly caused inside the oxide layer 211 and at theinterface between the oxide layer 211 and the separation layer 202.Thus, as illustrated in FIG. 8D, the oxide layer 211 might be attachedto the surfaces of the separation layer 202 and the separation layer 203after the separation. In FIG. 8D, the oxide layer 211 a attached on theseparation layer 203 side and the oxide layer 211 b attached on theseparation layer 202 side are illustrated. Note that the thickness ofthe attached oxide layer 211 a may be different from that of theattached oxide layer 211 b. Since separation is easily caused at theinterface between the oxide layer 211 and the separation layer 202, thethickness of the oxide layer 211 a on the separation layer 203 side islarger than that of the oxide layer 211 b on the separation layer 202side in many cases.

Bonding

Then, as illustrated in FIG. 8E, the substrate 101 is bonded to theseparation interface side of the separation layer 203 with an adhesivelayer 135 interposed therebetween. For the materials that can be usedfor the adhesive layer 135 and the substrate 101, the above descriptionof the adhesive layer 132 and the substrate 131 can be referred to.

Exposure of Wiring

Next, to expose part of a surface of the wiring 111 and part of asurface of the wiring 114, part of the substrate 131 and part of theadhesive layer 132 are removed and an opening is formed (FIG. 8F).

For example, in the case of using a resin as the substrate 131, amasking tape or the like is provide so as to surround the area for theopening, a solvent for dissolving the substrate 131 and the adhesivelayer 132 is dropped into the surrounded area, and the dissolvedsubstrate 131 and the dissolved adhesive layer 132 are removed; thus,the opening that exposes part of the wiring 111 or the wiring 114 can beformed. Alternatively, after cutting an indentation into an uppersurface of the substrate 131 around the area for the opening with acutting instrument such as a cutter, the substrate 131 and the adhesivelayer 132 are separated physically. Further alternatively, part of thesubstrate 131 and part of the adhesive layer 132 are removed byirradiation with laser light or the like.

Through the above-described process, a display device of one embodimentof the present invention can be manufactured.

Note that the method for forming the display portion 102, the wiring111, and the wiring 114 over the flexible substrate 101 is not limitedto the above-described method; the display portion 102, the wiring 111and the wiring 114 may be directly formed over the substrate 101. In thecase where the substrate 101 has heat resistance to the heat applied inthe formation process of the display portion 102, the wiring 111 or thewiring 114, the method of directly forming the display portion 102, thewiring 111 and the wiring 114 over the substrate 101 is preferable interms of process simplicity. In this case, the display portion 102, thewiring 111 and the wiring 114 are preferably formed in a state where thesubstrate 101 is fixed to a supporting member, in which case transfer ofthe element in an apparatus and between apparatuses for forming thedisplay portion 102, the wiring 111 and the wiring 114 can be easy.

Further, the combination of the materials of the separation layers canbe selected without being limited to the above example so thatseparation occurs at the interface between the separation layers or inthe separation layers. For example, a combination of low adhesivematerials such as metal and a resin may be employed.

The separation layer on the supporting substrate side is not necessaryin the case where separation can occur at an interface between thesupporting substrate and the separation layer on the display portionside. For example, glass is used as the supporting substrate, an organicresin such as polyimide is used as the separation layer on the displayportion side, and separation is performed by heating the organic resin.Alternatively, a metal layer may be provided between the supportingsubstrate and the separation layer on the display portion side formed ofan organic resin, and separation may be performed at the interfacebetween the metal layer and the separation layer by heating the metallayer by feeding a current to the metal layer.

This embodiment can be implemented in combination with any of the otherembodiments disclosed in this specification as appropriate.

Embodiment 3

In this embodiment, specific configuration examples of the displaydevice described in Embodiment 1 will be described with reference todrawings. Examples of an image display device to which an organic ELelement is used will be described below.

Configuration Example 1 of Display Device

FIG. 9 is a schematic cross-sectional view of a display device 300 witha top emission structure. The schematic top view of the display device300 of FIG. 9 corresponds to FIG. 1A, and FIG. 9 corresponds to aschematic cross-sectional view of the region including the displayportion 102, the wiring 111, and the connection terminal 112 in FIGS. 1Aand 1B.

The display device 300 includes the separation layer 203 over a flexiblesubstrate 354 with an adhesive layer 135 interposed therebetween. Thedisplay device 300 further includes, over the separation layer 203, thepixel portion 103 including a light-emitting element 340, the drivercircuit 104, the wiring 111, and the connection terminal 112. Further, aflexible substrate 353 is provided to face the substrate 354 with asealing layer 352 interposed therebetween.

The wiring 111 includes the first portion 121 and the second portion 122that have different thicknesses. The thick portion (the second portion122 in FIG. 9 ) of the wiring 111 has a stacked structure including thesame conductive film as the gate electrode of a transistor that isdescribed later and the same conductive film as the source electrode andthe drain electrode of the transistor. The thin portion (the firstportion 121 in FIG. 9 ) of the wiring 111 is formed of the sameconductive film as the source electrode and the drain electrode of thetransistor. In addition, part of the surface of the wiring 111 isexposed to form the connection terminal 112.

Examples of materials that can be used in an electrode and a wiring inthe transistor and the display element include a metal such as Al, Ti,Cr, Co, Ni, Cu, Y, Zr, Mo, Ru, Ag, Ta, or W, an alloy including themetal, and a nitride of the metal. In the case where the wiring 111 isformed by processing the same conductive film as the electrode and thewiring included in the transistor and the display element, because sucha conductive film is thin enough in most cases, destruction or a breakby bending does not occur even when the material of the conductive filmhas low ductility or low malleability.

FIG. 9 illustrates a circuit in which an n-channel transistor 311 and ann-channel transistor 312 are combined as an example of part of thedriver circuit 103. Note that the driver circuit 104 is not limited tothe circuit in which the n-channel transistors are combined and mayinclude a variety of circuits such as a CMOS circuit in which ann-channel transistor and a p-channel transistor are combined or acircuit in which p-channel transistors are combined.

FIG. 9 illustrates a cross-sectional structure of one pixel as anexample of the pixel portion 103. The pixel includes a switchingtransistor 313, a current control transistor 314, and a first electrode333 electrically connected to an electrode (a source electrode or adrain electrode) of the current control transistor 314. An insulatinglayer 319 is provided to cover an end portion of the first electrode333.

The light-emitting element 340 has a stacked structure in which thefirst electrode 333, an EL layer 335, and a second electrode 337 aresequentially stacked over an insulating layer 317. Since the displaydevice 300 described in this configuration example is a top emissiondisplay device, a light-transmitting material is used for the secondelectrode 337. A reflective material is preferably used for the firstelectrode 333. The EL layer 335 contains at least a light-emittingorganic compound. When voltage is applied between the first electrode333 and the second electrode 337 between which the EL layer 335 isinterposed so that current flows to the EL layer 335, the light-emittingelement 340 can emit light.

A separation layer 343 is provided on a surface of the flexiblesubstrate 353 which faces the substrate 354, with an adhesive layer 342interposed therebetween. In addition, a color filter 321 is provided onthe separation layer 343 in a position overlapping the light-emittingelement 340, and a black matrix 322 is provided in a positionoverlapping the insulating layer 319. The separation layer 343 is formedusing the same materials as the separation layer 203.

Note that a touch sensor may be formed by providing a wiring formed of atransparent conductive film over a surface of the substrate 353 whichdoes not face the substrate 354. A touch sensor formed over a flexiblesubstrate, which is not the substrate 353 or the substrate 354, may beprovided so as to overlap with the substrate on the light emission side.Further, in the case of employing a touch sensor including an opticalsensor, a plurality of photoelectric conversion elements are arranged ina matrix in the pixel portion 103.

The separation layer 203 and the separation layer 343 have functions ofinhibiting the diffusion of impurities contained in the substrate 354and the substrate 353, respectively. It is preferable that an insulatinglayer 316 and an insulating layer 318 which are in contact withsemiconductor layers of the transistors inhibit the diffusion ofimpurities into the semiconductor layers. These insulating layers can beformed using, for example, an oxide or a nitride of a semiconductor suchas silicon or a metal such as aluminum. A stack including such inorganicinsulating materials or a stack including such an inorganic insulatingmaterial and an organic insulating material may be used.

As the inorganic insulating material, for example, a material selectedfrom aluminum nitride, aluminum oxide, aluminum nitride oxide, aluminumoxynitride, magnesium oxide, gallium oxide, silicon nitride, siliconoxide, silicon nitride oxide, silicon oxynitride, germanium oxide,zirconium oxide, lanthanum oxide, neodymium oxide, and tantalum oxidecan be used. A single layer or a stack including any of the abovematerials may be formed. In this specification, the nitride oxide refersto a material containing a larger amount of nitrogen than oxygen, andthe oxynitride refers to a material containing a larger amount of oxygenthan nitrogen. The element content can be measured by, for example,Rutherford back scattering spectrometry (RBS). As the inorganicinsulating material, a high-k material such as hafnium silicate(HfSiO_(x)), hafnium silicate to which nitrogen is added(HfSi_(x)O_(y)N_(z)), hafnium aluminate to which nitrogen is added(HfAl_(x)O_(y)N_(z)), hafnium oxide, or yttrium oxide may be used.

The separation layer 343 can be formed by applying the method describedin Embodiment 2. That is, the structure illustrated in FIG. 9 can beobtained in the following manner: the separation layer, the oxide layer,and the separation layer 343 are formed over the supporting substrate,the color filter 321 and the black matrix 322 are formed over theseparation layer 343, separation is performed, and then the substrate353 is bonded to the back side of the separation layer 343 with theadhesive layer 342 interposed therebetween.

As illustrated in FIG. 9 , the oxide layer 211 a and the oxide layer 341may be provided between the separation layer 203 and the adhesive layer135, and between the separation layer 343 and the adhesive layer 342,respectively. The oxide layer 211 a and the oxide layer 341 areextremely thin and have light-transmitting properties, and thus hardlydecrease emission efficiency even when provided on the side where lightemitted from the light-emitting element 340 is extracted.

It is preferable that the separation layer 203 provided with thetransistors and the like and the separation layer 343 provided with thecolor filter 321 and the like be bonded to each other with the sealinglayer 352 in the state where the supporting substrates are attached tothe respective separation layers before separation is performed. It ispreferable that the separation layers be separated from the respectivesubstrates after the bonding. In the case where the color filter 321 andpixels need to be aligned with high accuracy particularly as in thedisplay device including the high-definition display portion 103, thelayers are bonded while being fixed to supporting substrates such asglass substrates, whereby the color filter 321 and the pixels can bealigned with high accuracy. By the above-described method, ahigh-definition, flexible display device can be manufactured.

Note that although FIG. 9 illustrates the case where the light-emittingelement is used as a display element, one embodiment of the presentinvention is not limited thereto. It is possible to use a liquid crystalelement, an electrophoretic element (electronic paper), or the like as adisplay element. An electrophoretic element is preferable for oneembodiment of a flexible display device because a backlight is notrequired.

Configuration Example 2 of Display Device

In this configuration example, a display device with a bottom-emissionstructure is described. Note that the same parts as those in StructureExample 1 are not described here.

FIG. 10 is a schematic cross-sectional view of a display device 350described in this structure example.

The display device 350 is different from the display device 300described in Structure Example 1 mainly in the following points. In thedisplay device 350, a color filter 321 is provided between the substrate354 and the light-emitting element 340. In addition, the flexiblesubstrate 353 is in direct contact with the sealing layer 352, and theseparation layer 343 and the adhesive layer 342 that are provided in thedisplay device 300 are not provided.

In the light-emitting element 340, a light-transmitting material is usedfor the first electrode 333, and a reflective material is used for thesecond electrode 337. Thus, light emission from the EL layer 335 istransmitted through the substrate 354.

Further, the color filter 321 is provided at the position over theinsulating layer 318 covering transistors which overlaps with thelight-emitting element 340. The insulating layer 317 is provided tocover the color filter 321.

A material that is not permeable to an impurity such as water from theoutside of the substrate 353 is preferably used as the substrate 353.Alternatively, a film formed of the above-discribed insulating material,which has a function of inhibiting the diffusion of impurities, ispreferably provided on a surface of the substrate 253 which is incontact with the sealing layer 352.

Materials and Formation Methods

Materials and formation methods which can be used for the componentsdescribed above will be described below.

Flexible Substrate

As a material for the flexible substrate, an organic resin, a glasssubstrate thin enough to have flexibility, or the like can be used.

Examples of such materials are polyester resins such as polyethyleneterephthalate (PET) and polyethylene naphthalate (PEN), apolyacrylonitrile resin, a polyimide resin, a polymethyl methacrylateresin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, apolyamide resin, a cycloolefin resin, a polystyrene resin, a polyamideimide resin, and a polyvinyl chloride resin. In particular, a materialwhose thermal expansion coefficient is low, for example, lower than orequal to 30×10⁻⁶/K is preferable, and a polyamide imide resin, apolyimide resin, or PET can be suitably used. A substrate in which afibrous body is impregnated with a resin (also referred to as prepreg)or a substrate whose thermal expansion coefficient is reduced by mixingan inorganic filler with an organic resin can also be used.

In the case where a fibrous body is included in the above material, ahigh-strength fiber of an organic compound or an inorganic compound isused as the fibrous body. The high-strength fiber is specifically afiber with a high tensile modulus of elasticity or a fiber with a highYoung's modulus. Typical examples thereof include a polyvinyl alcoholbased fiber, a polyester based fiber, a polyamide based fiber, apolyethylene based fiber, an aramid based fiber, a polyparaphenylenebenzobisoxazole fiber, a glass fiber, and a carbon fiber. As an exampleof the glass fiber, a glass fiber using E glass, S glass, D glass, Qglass, or the like can be given. These fibers may be used in a state ofa woven fabric or a nonwoven fabric, and a structure body in which thisfibrous body is impregnated with a resin and the resin is cured may beused as the flexible substrate. The structure body including the fibrousbody and the resin is preferably used as the flexible substrate, inwhich case the reliability against bending or breaking due to localpressure can be increased.

A material capable of transmitting light emitted from the EL layer 335is used for the flexible substrate through which light emitted from thelight-emitting element 340 is transmitted. To improve the outcouplingefficiency of the material provided on the light extraction side, therefractive index of the flexible, light-transmitting material ispreferably high. For example, a substrate obtained by dispersing aninorganic filler having a high refractive index into an organic resincan have a higher refractive index than the substrate formed of only theorganic resin. In particular, an inorganic filler having a particlediameter as small as 40 nm or less is preferably used, in which casesuch a filler can maintain optical transparency.

Since the substrate provided on the side opposite to the side throughwhich light is transmitted does not need to have a light-transmittingproperty, a metal substrate or the like can be used as well as the abovesubstrates. To obtain flexibility and bendability, the thickness of ametal substrate is preferably greater than or equal to 10 μm and lessthan or equal to 200 μm, further preferably greater than or equal to 20μm and less than or equal to 50 μm. Although there is no particularlimitation on a material of the metal substrate, it is preferable touse, for example, aluminum, copper, nickel, a metal alloy such as analuminum alloy or stainless steel. A conductive substrate containing ametal or an alloy material is preferably used as the flexible substrateprovided on the side through which light is not transmitted, in whichcase heat dissipation of the heat generated from the light-emittingelement 340 can be increased.

In the case where a conductive substrate is used, it is preferable touse a substrate subjected to insulation treatment in such a manner thata surface of the substrate is oxidized or an insulating film is formedover the surface of the substrate. For example, an insulating film maybe formed over the surface of the conductive substrate by anelectrodeposition method, a coating method such as a spin-coating methodor a dip method, a printing method such as a screen printing method, ora deposition method such as an evaporation method or a sputteringmethod. Alternatively, the surface of the substrate may be oxidized bybeing exposed to an oxygen atmosphere or heated in an oxygen atmosphereor by an anodic oxidation method.

In the case where the flexible substrate has an uneven surface, aplanarization layer may be provided to cover the unevenness so that aflat insulating surface is formed. An insulating material can be usedfor the planarization layer; an organic material or an inorganicmaterial can be used. The planarization layer can be formed by adeposition method such as a sputtering method, a coating method such asa spin-coating method or a dip method, a discharging method such as anink jet method or a dispensing method, a printing method such as ascreen printing method, or the like.

As the flexible substrate, a material in which a plurality of layers arestacked can also be used. For example, a material in which two or morekinds of layers formed of an organic resin are stacked, a material inwhich a layer formed of an organic resin and a layer formed of aninorganic material are stacked, or a material in which two or more kindsof layers formed of an inorganic material are stacked is used. With alayer formed of an inorganic material, moisture and the like areprevented from entering the inside, resulting in improved reliability ofthe light-emitting device.

As the inorganic material, an oxide material, a nitride material, or anoxynitride material of a metal or a semiconductor, or the like can beused. For example, silicon oxide, silicon nitride, silicon oxynitride,aluminum oxide, aluminum nitride, or aluminum oxynitride may be used.

For example, in the case where a layer formed of an organic resin and alayer formed of an inorganic material are stacked, the layer formed ofan inorganic material can be formed over or under the layer formed of anorganic resin by a sputtering method, a CVD method, a coating method, orthe like.

Light-Emitting Element

In the light-emitting element 340, a light-transmitting material capableof transmitting light emitted from the EL layer 335 is used for anelectrode provided on the side through which light is transmitted.

As the light-transmitting material, indium oxide, indium oxide-tinoxide, indium oxide-zinc oxide, zinc oxide, zinc oxide to which galliumis added, or the like can be used. Graphene may also be used. Theconductive layer of the above-described electrode may be formed using ametal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, andtitanium; or an alloy material containing any of these metal materials.A nitride of the metal material (e.g., titanium nitride) or the like mayalso be used. In the case of using the metal material (or the nitridethereof), the thickness is set small enough to be able to transmitlight. Alternatively, a stack including any of the above materials canalso be used as the conductive layer of the above-described electrode.For example, a stacked film including a silver-magnesium alloy andindium oxide-tin oxide is preferably used, in which case electricalconductivity can be increased.

Such an electrode is formed by an evaporation method, a sputteringmethod, or the like. A discharging method such as an ink-jet method, aprinting method such as a screen printing method, or a plating methodmay be used.

Note that when the above conductive oxide having a light-transmittingproperty is formed by a sputtering method, the use of a depositionatmosphere containing argon and oxygen allows the light-transmittingproperty to be increased.

Further, in the case where the conductive oxide film is formed over theEL layer, a first conductive oxide film formed under an atmospherecontaining argon with a reduced oxygen concentration and a secondconductive oxide film formed under an atmosphere containing argon andoxygen are preferably stacked, in which case film formation damage tothe EL layer can be reduced. In this case, in the formation of the firstconductive oxide film, it is preferable to use an argon gas with highpurity, for example, an argon gas whose dew point is lower than or equalto −70° C., further preferably lower than or equal to −100° C.

A material capable of reflecting light emitted from the EL layer 335 ispreferably used for the electrode provided on the side opposite to theside through which light is transmitted.

As the light-reflecting material, for example, a metal such as aluminum,gold, platinum, silver, nickel, tungsten, chromium, molybdenum, iron,cobalt, copper, or palladium or an alloy containing any of these metalscan be used. Alternatively, lanthanum, neodymium, germanium, or the likemay be added to the metal or the alloy. In addition, any of thefollowing can be used: alloys containing aluminum (aluminum alloys) suchas an alloy of aluminum and titanium, an alloy of aluminum and nickel,and an alloy of aluminum and neodymium; and alloys containing silversuch as an alloy of silver and copper, an alloy of silver, palladium,and copper, and an alloy of silver and magnesium. An alloy of silver andcopper is preferable because of its high heat resistance. Further, bystacking a metal film or a metal oxide film in contact with an aluminumalloy film, oxidation of the aluminum alloy film can be suppressed.Examples of a material for the metal film or the metal oxide film aretitanium and titanium oxide. Further alternatively, a stack including afilm containing any of the above light-transmitting materials and a filmcontaining any of the above metal materials may be used. For example, astacked film including silver and indium oxide-tin oxide, a stacked filmincluding a silver-magnesium alloy and indium oxide-tin oxide, or thelike can be used.

Such an electrode is formed by an evaporation method, a sputteringmethod, or the like. A discharging method such as an ink-jet method, aprinting method such as a screen printing method, or a plating methodmay be used.

The EL layer 335 includes at least a layer containing a light-emittingorganic compound (hereinafter also called a light-emitting layer), andmay be either a single layer or a stack including a plurality of layers.One example of the structure in which a plurality of layers is stackedis a structure in which a hole-injection layer, a hole-transport layer,a light-emitting layer, an electron-transport layer, and anelectron-injection layer are stacked in this order from an anode side.Note that all of these layers except the light-emitting layer are notnecessarily provided in the EL layer 335. Further, multiple layers ofany of these layers may be provided. Specifically, in the EL layer 335,a plurality of light-emitting layers may overlap each other or anotherhole-injection layer may overlap the electron-injection layer.Furthermore, another component such as an electron-relay layer may beadded as appropriate as an intermediate layer, in addition to the chargegeneration layer. Alternatively, a plurality of light-emitting layersexhibiting different colors may be stacked. For example, a whiteemission can be obtained by stacking two or more layers emitting lightof complementary colors.

The EL layer 335 can be formed by a vacuum evaporation method, adischarging method such as an ink-jet method or a dispensing method, ora coating method such as a spin-coating method.

Adhesive Layer and Sealing Layer

As the adhesive layer and the sealing layer, it is possible to use, forexample, a gel or a curable material such as a two-component-mixturetype resin which is curable at room temperature, a thermosetting resin,or a light curable resin. For example, an epoxy resin, an acrylic resin,a silicone resin, a phenol resin, polyimide, polyvinyl chloride (PVC),polyvinyl butyral (PVB), or ethylene vinyl acetate (EVA) can be used. Inparticular, a material with low moisture permeability, such as an epoxyresin, is preferable.

A drying agent may be contained in the adhesive layer and the sealinglayer. For example, a substance that adsorbs moisture by chemicaladsorption, such as oxide of an alkaline earth metal (e.g., calciumoxide or barium oxide), can be used. Alternatively, a substance thatadsorbs moisture by physical adsorption, such as zeolite or silica gel,may be used as the drying agent. In the case where the drying agent isapplied to a lighting device, when a granular drying agent is employed,light emitted from the light-emitting element 340 is diffusely reflectedby the drying agent; thus, a highly reliable light-emitting device withimproved viewing angle dependence, which is particularly useful forlighting and the like, can be achieved.

Color Filter and Black Matrix

The color filter 321 is provided in order to adjust the color of lightemitted from the light-emitting element 340 to increase the colorpurity. For example, in a full-color display device using whitelight-emitting elements, a plurality of pixels provided with colorfilters of different colors are used. In that case, the color filtersmay be those of three colors of red (R), green (G), and blue (B) or fourcolors (yellow (Y) in addition to these three colors). Further, a white(W) pixel may be added to R, G, and B pixels (and a Y pixel). That is,color filters of four colors (or five colors) may be used.

The black matrix 322 is provided between the adjacent color filters 321.The black matrix 322 shields a pixel from light emitted from thelight-emitting element 340 in an adjacent pixel, thereby preventingcolor mixture between the adjacent pixels. When the color filter 321 isprovided so that its end portion overlaps the black matrix 322, lightleakage can be reduced. The black matrix 322 can be formed using amaterial that blocks light emitted from the light-emitting element 340,for example, a metal or an organic resin containing a pigment. Note thatthe black matrix 322 may be provided in a region other than the pixelportion 103, for example, in the driver circuit 104.

An overcoat may be formed to cover the color filter 321 and the blackmatrix 322. The overcoat protects the color filter 321 and the blackmatrix 322 and suppresses diffusion of impurities included in the colorfilter 321 and the black matrix 322. The overcoat is formed using amaterial that transmits light emitted from the light-emitting element340, and can be formed using, for example, an inorganic insulating filmor an organic insulating film.

The materials and the formation methods have been described so far.

This embodiment can be implemented in combination with any of the otherembodiments disclosed in this specification as appropriate.

Embodiment 4

In this embodiment, examples of an electronic device that includes adisplay device of one embodiment of the present invention will bedescribed.

The display device of one embodiment of the present invention has abendable display surface. Examples of the electronic device in which thedisplay device can be incorporated include television sets (alsoreferred to as televisions or television receivers), monitors ofcomputers or the like, digital cameras, digital video cameras, digitalphoto frames, mobile phones (also referred to as cell phones or cellularphones), portable game consoles, personal digital assistants, audioreproducing devices, and large-sized game machines such as pachinkomachines. In addition, a lighting device or a display device can beincorporated along a curved inside/outside wall surface of a house or abuilding or a curved interior/exterior surface of a car.

FIG. 11A illustrates an example of a mobile phone. A mobile phone 7400is provided with a display portion 7402 incorporated in a housing 7401,operation buttons 7403, an external connection port 7404, a speaker7405, a microphone 7406, and the like. Note that the mobile phone 7400is manufactured by using the display device of one embodiment of thepresent invention for the display portion 7402.

When the display portion 7402 is touched with a finger or the like, datacan be input into the mobile phone 7400 in FIG. 11A. Further, operationssuch as making a call and inputting text can be performed by touch onthe display portion 7402 with a finger or the like.

The power can be turned on or off with the operation buttons 7403. Inaddition, types of images displayed on the display portion 7402 can beswitched; for example, switching images from a mail creation screen to amain menu screen is performed with the operation buttons 7403.

Here, the display portion 7402 includes the display device of oneembodiment of the present invention. Thus, images can be displayed onthe bent display surface, and the mobile phone can have highreliability.

FIG. 11B illustrates an example of a wristband-type display device. Aportable display device 7100 includes a housing 7101, a display portion7102, an operation button 7103, and a sending and receiving device 7104.

The portable display device 7100 can receive a video signal with thesending and receiving device 7104 and can display the received video onthe display portion 7102. In addition, with the sending and receivingdevice 7104, the portable display device 7100 can send an audio signalto another receiving device.

With the operation button 7103, power ON/OFF, switching of displayedvideos, adjusting volume, and the like can be performed.

Here, the display portion 7102 includes the display device of oneembodiment of the present invention. Thus, the portable display devicecan have a bent display portion and have high reliability.

FIG. 11C illustrates an example of a wrist-watch-type portableinformation terminal. A portable information terminal 7200 includes ahousing 7201, a display portion 7202, a band 7203, a buckle 7204, anoperation button 7205, an input output terminal 7206, and the like.

The portable information terminal 7200 is capable of executing a varietyof applications such as mobile phone calls, e-mailing, viewing andediting texts, music reproduction, Internet communication, and acomputer game.

The display surface of the display portion 7202 is bent, and images canbe displayed on the bent display surface. Further, the display portion7202 includes a touch sensor, and operation can be performed by touchingthe screen with a finger, a stylus, or the like. For example, bytouching an icon 7207 displayed on the display portion 7202, applicationcan be started.

With the operation button 7205, a variety of functions such as powerON/OFF, ON/OFF of wireless communication, setting and cancellation ofmanner mode, and setting and cancellation of power saving mode can beperformed. For example, the functions of the operation button 7205 canbe set freely by setting the operation system incorporated in theportable information terminal 7200.

Further, the portable information terminal 7200 can employ near fieldcommunication. In that case, for example, mutual communication betweenthe portable information terminal 7200 and a headset capable of wirelesscommunication can be performed, and thus hands-free calling is possible.

Moreover, the portable information terminal 7200 includes the inputoutput terminal 7206, and data can be directly transmitted to andreceived from another information terminal via a connector. Powercharging through the input output terminal 7206 is possible. Note thatthe charging operation may be performed by wireless power feedingwithout using the input output terminal 7206.

The display device of one embodiment of the present invention can beused in the display portion 7202 of the portable information terminal7200.

The display device of one embodiment of the present invention can beused in display portions of the electronic devices described in thisembodiment. Therefore, the electronic devices can each have highreliability, display images on the curved surface, and have a short sideframe.

This embodiment can be implemented in combination with any of the otherembodiments disclosed in this specification as appropriate.

EXPLANATION OF REFERENCE

100: display device, 101: substrate, 102: display portion, 103: pixelportion, 104: driver circuit, 104 a: driver circuit, 104 b: drivercircuit, 104 c: driver circuit, 104 d: driver circuit, 104 e: drivercircuit, 104 f: driver circuit, 104 g: driver circuit, 104 h: drivercircuit, 110: bending portion, 111: wiring, 111 a: wiring, 111 b:wiring, 112: connection terminal, 113: IC, 114: wiring, 120: bendingportion, 121: first portion, 122: second portion, 131: substrate, 132:adhesive layer, 133: ACF, 134: bump, 135: adhesive layer, 141: curvedsurface, 142: tangent line, 143: bending direction, 144: line, 145:surface, 151: wiring, 201: supporting substrate, 202: separation layer,203: separation layer, 211: oxide layer, 211 a: oxide layer, 211 b:oxide layer, 300: display device, 311: transistor, 312: transistor, 313:transistor, 314: transistor, 316: insulating layer, 317: insulatinglayer, 318: insulating layer, 319: insulating layer, 321: color filter,322: black matrix, 333: electrode, 335: EL layer, 337: electrode, 340:light-emitting element, 341: oxide layer, 342: adhesive layer, 343:separation layer, 350: display device, 352: sealing layer, 353:substrate, 354: substrate, 7100: portable display device, 7101: housing,7102: display portion, 7103: operation button, 7104: sending andreceiving device, 7200: portable information terminal, 7201: housing,7202: display portion, 7203: band, 7204: buckle, 7205: operation button,7206: input output terminal, 7207: icon, 7400: mobile phone, 7401:housing, 7402: display portion, 7403: operation button, 7404: externalconnection port, 7405: speaker, 7406: microphone.

This application is based on Japanese Patent Application serial no.2013-045119 filed with Japan Patent Office on Mar. 7, 2013, the entirecontents of which are hereby incorporated by reference.

1. An electronic device comprising: a display device, the display devicecomprising: a protruding portion protruding from part of a short-side ofthe display device; a first substrate having flexibility; an oxide layerover the first substrate; a first conductive layer and a secondconductive layer over the oxide layer; a first insulating layer over thefirst conductive layer and the second conductive layer; a thirdconductive layer over the first insulating layer and overlapping withthe first conductive layer; a fourth conductive layer over the firstinsulating layer; a light-emitting element over the fourth conductivelayer; an adhesive layer over the light-emitting element; and a secondsubstrate over the adhesive layer, wherein the third conductive layer iselectrically connected to the first conductive layer, wherein the thirdconductive layer is configured to function as one of a plurality offirst wirings, wherein the second conductive layer is configured tofunction as a gate electrode of a first transistor, wherein the fourthconductive layer is configured to function as one of a source electrodeand a drain electrode of the first transistor, wherein the thirdconductive layer and the fourth conductive layer are formed from a samelayer, wherein the protruding portion comprises a connection terminaland a bending portion, wherein the bending portion is bent and theprotruding portion is folded back so that a first portion of a firstsurface of the first substrate faces a second portion of the firstsurface of the first substrate, whereby a surface of the connectionterminal overlaps with a back side of a display portion, wherein asource driver circuit provided over the protruding portion overlaps withthe back side of the display portion, and wherein the display device isincorporated into the electronic device with the bending portion foldedback.
 2. An electronic device comprising: a display device, the displaydevice comprising: a protruding portion protruding from part of ashort-side of the display device; a first substrate having flexibility;an oxide layer over the first substrate; a first conductive layer and asecond conductive layer over the oxide layer; a first insulating layerover the first conductive layer and the second conductive layer; a thirdconductive layer over the first insulating layer and overlapping withthe first conductive layer; a fourth conductive layer over the firstinsulating layer; a light-emitting element over the fourth conductivelayer; an adhesive layer over the light-emitting element; and a secondsubstrate over the adhesive layer, wherein the third conductive layer iselectrically connected to the first conductive layer, wherein the thirdconductive layer is configured to function as one of a plurality offirst wirings, wherein the second conductive layer is configured tofunction as a gate electrode of a first transistor, wherein the fourthconductive layer is configured to function as one of a source electrodeand a drain electrode of the first transistor, wherein the thirdconductive layer and the fourth conductive layer are formed from a samelayer, wherein the protruding portion comprises a connection terminaland a bending portion, wherein the bending portion is bent and theprotruding portion is folded back so that a first portion of a firstsurface of the first substrate faces a second portion of the firstsurface of the first substrate, whereby a surface of the connectionterminal overlaps with a back side of a display portion, wherein asource driver circuit provided over the protruding portion overlaps withthe back side of the display portion, wherein the display device isincorporated into the electronic device with the bending portion foldedback, wherein, in a short-side direction of the display device, each oftwo end portions of a short-side of the protruding portion is providedfarther inside than end portions of the short-side of the displaydevice, and wherein the plurality of first wirings has a regioncomprising an opening and a branching portion where the plurality offirst wirings branches into a plurality of second wirings with theopening therebetween.
 3. An electronic device comprising: a displaydevice, the display device comprising: a protruding portion protrudingfrom part of a short-side of the display device; a first substratehaving flexibility; an oxide layer over the first substrate; a firstconductive layer and a second conductive layer over the oxide layer; afirst insulating layer over the first conductive layer and the secondconductive layer; a third conductive layer over the first insulatinglayer and overlapping with the first conductive layer; a fourthconductive layer over the first insulating layer; a light-emittingelement over the fourth conductive layer; an adhesive layer over thelight-emitting element; and a second substrate over the adhesive layer,wherein the third conductive layer is electrically connected to thefirst conductive layer, wherein the third conductive layer is configuredto function as one of a plurality of first wirings, wherein the secondconductive layer is configured to function as a gate electrode of afirst transistor, wherein the fourth conductive layer is configured tofunction as one of a source electrode and a drain electrode of the firsttransistor, wherein the third conductive layer and the fourth conductivelayer are formed from a same layer, wherein the protruding portioncomprises a connection terminal and a bending portion, wherein thebending portion is bent and the protruding portion is folded back sothat a first portion of a first surface of the first substrate faces asecond portion of the first surface of the first substrate, whereby asurface of the connection terminal overlaps with a back side of adisplay portion, wherein a source driver circuit provided over theprotruding portion overlaps with the back side of the display portion,wherein the display device is incorporated into the electronic devicewith the bending portion folded back, wherein, in a short-side directionof the display device, each of two end portions of a short-side of theprotruding portion is provided farther inside than end portions of theshort-side of the display device, wherein, in the case where the displaydevice is provided so that the protruding portion is located on theshort-side of the display device without folding the protruding portionback, the plurality of first wirings that pass through the bendingportion is provided from each of a first portion, a second portion, anda third portion of the short-side of the display device, wherein theplurality of first wirings is provided so as to come together from eachof the first portion, the second portion, and the third portion of theshort-side of the display device toward the protruding portion, whereinthe plurality of first wirings has a region comprising an opening and abranching portion where the plurality of first wirings branches into aplurality of second wirings with the opening therebetween, and whereinthe bending portion is curved to overlap with the branching portion.